This invention relates to an automatic door adapted to be driven to open and close by means of an electric motor, and more particularly to an automatic door in which the door body can be automatically closed and locked at the closing-stop point thereof when the supply of electric power to the electric motor is interrupted.
Automatic doors comprise generally a belt extending around a drive pulley located on one side of a door opening and adapted to be driven by a motor and a driven pulley located on the other side of the door opening, the belt being connected to the door body, and the automatic doors are arranged such that the door body can be moved to its opening- or closing-stop point by allowing the drive pulley to be rotated forwardly or reversely. Therefore, when the main electric power supply for supplying power to the motor is broken, the motor is stopped thereby stopping the door body immediately at the position as it is. As a result, the automatic door remains open.
Heretofore, as to the apparatus for moving automatic doors to their opening- and closing-stop points in case of emergency, there has been known an emergency door opening and closing apparatus utilizing a weight. In such an apparatus, there is a fear that, when the door body is opened or closed in case of emergency, the stopper having a chain or rope connected to a weight may move quickly towards and collide against the stopper device provided on the door causing a high impact force and a shock sound giving a damage to the apparatus.
Further, the Japanese Patent Publication No. SHO 60-16552 discloses an apparatus for automatically moving a door body in the direction of opening closing-stop point thereof by the resilient force of a plate spring when the main power supply is switched off so as to move the automatic door to its opening- or closing-stop point. However, in both the apparatus mentioned earlier and the apparatus disclosed in the above Japanese Patent publication, the automatic door cannot be automatically locked at its closing-stop point. For example, even if the main power supply installed in an office building is switched off when leaving the office, each of the locking apparatuses installed on all doors need to be locked manually, which is very troublesome operation.